The present invention relates to a radiation tomography apparatus and a scan condition setting device. In particular, it relates to a radiation tomography apparatus which produces a main scan image about an imaging area of a subject by performing a main scan in which radiation beams are applied to the imaging area of the subject and the radiation beams having passed through the imaging area of the subject are detected. Also, it relates to a scan condition setting device for setting a main scan condition for the main scan.
The radiation tomography apparatus such as an X-ray CT (Computed Tomography) apparatus scans a subject with radiant rays such as an X-ray and, being based on projection data obtained by the scan, produces a tomographic image of a slice surface of the subject. Such a radiation tomography apparatus is used for wide variety of purposes including medical purposes and industrial purposes.
Before performing a main scan to produce a tomographic image, in order to set a main scan condition, the X-ray CT apparatus performs a scout scan and produces a scout image, which, is a through view of the subject.
An operator refers to the scout image produced by the scout scan and inputs scan parameters for performing the main scan. Then, the operator sets scan conditions such as a slice position corresponding to a slice surface where a tomographic image is produced, a scanning method, etc. Then, according to the main scan conditions so set, the main scan is performed and a tomographic image about the slice surface of the subject is produced (See, for example, Japanese Unexamined Patent Publication No. 2005-58651 and Japanese Unexamined Patent Publication No. Hei 8(1996)-289887).
Incidentally, when the main scan by a helical scanning method is given to an imaging area including a breast of a female subject, a shield for shielding X-rays is placed on the breast of the subject so that radiation exposure on a highly radiosensitive mammary gland can be reduced and the X-rays can effectively be utilized.
In such a case, however, since the shield absorbs X-rays, it sometimes degraded the quality of the tomographic image produced by the main scan. Therefore, in some cases, it was difficult to effectively use radiant rays such as an X-ray and to improve image quality at the same time. In addition, similar inconveniences took place when there were highly radiosensitive portions near the body surface of the subject such as the crystalline lens in a head of the subject and a thyroid gland in a neck of the subject.
In view of the above, it is an object of the present invention is to provide a radiation tomography apparatus and a scan condition setting device capable of utilizing radiation effectively and improving image quality.